It has become apparent that emitter-coupled logic (ECL) is playing an increasing role in logic design. ECL is taking the form of gate arrays, translators, current/differential drivers, complex processors, programmable array logic (PAL) devices and "glue" logic. A general problem associated with the use of ECL is its communication to devices of the TTL logic family. As one example, ECL arrays are commonly connected to TTL memories commonly used in large or mainframe computer systems. Other examples include the connection of ECL circuits to TTL peripheral devices.
ECL to TTL voltage level translators have been previously devised. Conventional ECL to TTL voltage level translators are typified by U.S. Pat. No. 4,644,194 issued to M. Birrittella et al. While published as an ECL to TTL voltage level translator, this device actually only displaces the voltage level from an ECL signal, generally ranging from a low voltage of -1.7 volts to a high voltage of -0.9 volts, to a voltage of from 0.5 V.sub.BE to 1.5 V.sub.BE, where V.sub.BE is the base-emitter voltage across an output bipolar transistor. The output signal derived from this circuit is not referenced to high and low TTL voltage supplies. Further processing of the output of this circuit would therefore be necessary before the signal could be used in TTL logic. A conversion circuit for converting a true ECL signal to a true TTL signal has yet been developed.
Conventionally, TTL or ECL "glue logic" is used to provide flexibility and design logic to provide mapping, decoding, general logic functions and synchronization. In many designs, it is not practical to include all electrical functions within a gate array or fixed logic device.
From the above, it can be seen that a need exists for a voltage level translation circuit that converts true input ECL voltage levels to a true TTL output signal. Further, a need exists for such a translation circuit in combination with an interfacing logic device.